Preparation of aromatic dihydro dicarboxylic acids



Patented Nov. 1, 1938 UNITED STATES PATENT OFFICE Joseph FredericWalker, Niagara Falls, N. Y., as-

signor to E. I. du Pont de Nemonrs & Company, Wilmington, Del., acorporation of Delaware N0 Drawing. Application November 19, 1936,Serial No. 111,676

16 Claims.

This invention relates to the preparation of organic acids andparticularly to a method for preparing, separating, and isolatingdicarboxylic acids of dihydroaromatic hydrocarbons containing twobenzene nuclei per molecule.

Carboxyl derivatives of partially hydrogenated polycyclic aromatichydrocarbons may be prepared by reacting an alkali metal with apolycyclic aromatic hydrocarbon in a suitable solvent medium to form analkali metal hydrocarbon addition product and subsequently reacting saidaddition product with carbon dioxide to produce the alkali metal saltsof the corresponding carboxyl derivatives. For example, if naphthaleneis reacted with sodium in this manner, a disodium naphthalene additioncompound having the empirical formula C'mHsNaz is formed. This additionproduct is soluble in the solvent medium in which it is formed, causinga green color therein. Similar alkali metal addition compounds of otherpolycyclic aromatic hydrocarbons may be formed by substantially the samemethod; all of these addition products are more or less soluble in thesolvent mediums used and their presence is indicated by a distinctcoloration of the solvent. If the colored solution of the alkali metaladdition compound is treated with carbon dioxide the color is dischargedand the sodium salts of the corresponding carboxyl derivatives areprecipitated. For example, when disodium naphthalene is reacted withcarbon dioxide, the product is a mixture of the sodium salts of isomericacids having the formula C10Ha(COOH) 2. These acids,

N which may be termed .dihydronaphthalene dicarboxylic acids are thedicarboxyl derivatives of dihydronaphthalene. They probably occur in twoisomeric forms which may be represented by the graphic formulas:

COOH

HVOOOH a m OUOOOH H COOH 1, 4-dihydronaphthalene l,2-dihyd1'onapl1thalene 1, i-dicarboxylic acid is described by Schlenkand Bergmann, Liebigs Annalen, volume 463, pages 90 and 95. The methodsof carrying out these reactions using certain ingredients as solventmedia which facilitate the reaction of sodium and other alkali 5 metalswith polycyclic aromatic hydrocarbons in general are described in U. S.Patent 2,027,000 issued January 7, 1936 to Norman D. Scott. Methods ofpreparing these carboxyl derivatives of partially hydrogenatedpolycyclic aromatic hydrocarbons are described and claimed in the aboveScott patent and in my U. S. Patent 2,033,056 issued March 3, 1936.

As indicated above, salts of two isomeric dicarboxylic acids are formedwhen an alkali metal addition compound of a polycyclic aromatichydrocarbon is treated with carbon dioxide. A general characteristic 'ofthose hydrocarbons, such as naphthalene and diphenyl, which have twobenzene nuclei per molecule is that the acids 20 formed uponcarboxylating the alkali metal addition compound of the hydrocarbonconsists of a high melting and a low melting dihydro dicarboxylic acid.I

One object of the present invention is to pro- Vide an improved methodof preparing dihydro dicarboxylic acids of polycyclic aromatichydrocarbons having two benzene nuclei per molecule. Another object isto provide a method of isolating separately such acids. A further objectis to provide a method for rearranging the so-called low melting dihydrodicarboxylic acid of polycyclic aromatic hydrocarbons having two benzenenuclei per molecule so as to form a product which may be easily andeconomically isolated in comparatively pure form, or as a mixture withthe so-called high melting acid. Other objects will be hereinafterapparent.

The acids produced from those hydrocarbons having more than two benzenenuclei per molecule generally are readily isolated as a mixture fromtheir salts since both acids whose salts are primarily formed uponcarboxylating the alkali metal addition compound are sparingly solublein water. 0n the other hand, I have discovered that the acids producedfrom those hydrocarbons having only two benzene nuclei per molecule, e.g., naphthalene and diphenyl and their substituted derivatives, are noteasily isolated as a mixture from their salts. For example, in the 5case of the naphthalene derivatives, I have found that whereas the1,4-dicarboxylic acid is only slightly soluble in and crystallizesreadily from water, the 1,2-dicarboxylic acid is rather soluble in andcrystallizes with difiiculty from water.

The above differences in the properties of the two acids derived fromthose hydrocarbons having two benzene nuclei per molecule afford amethod for isolating the two acids separately from their salts.Accordingly, one modification of my invention comprises an improvedmethod for preparing these acids in isolated form. The isolation may beaccomplished by dissolving in water the salts of the acids which areformed by carboxylating the alkali metal addition compound of thehydrocarbon and acidifying the resulting solution with a suitable strongacid, e. g., hydrochloric or sulfuric acid. By this treatment theinsoluble high melting acid is precipitated while the low melting acidremains in solution. The former acid may be removed by filtration andfreed from traces of the low melting acid by thorough washing with warmwater. The low melting acid may be isolated from the combined filtrateand washings by any of several methods, for example, by extraction witha suitable solvent, e. g., ether, or by the formation of an insolublesalt such as the calcium salt from which the acid may be isolated in theusual manner. A further method for isolating the acid from the filtrateis to salt it out with sodium chloride. This method is illustrated inthe following example.

Example I the 1,2-dicarboxylic acid. The isolated acid was then washedthoroughly with cold water. The solubilities of the two products inwater ar approximately as follows:

Grams of acid per 100 cc. of solution At 25 C. At 95-100 C.

1, 4-dicarboxy1ic acid. 0. 14 1.7 1, 2-dicarboxylic acid. 2. 48

The above illustrated method affords a suitable manner for isolatingseparately the individual acids primarily formed by carboxylating thealkali metal addition compound. However, it is frequently desired toisolate dihydro dicarboxylic acids either in the form of a mixture orseparately as comparatively pure acids by a more direct and lessinvolved method. Accordingly, an important modification of my inventionrelates to such a method.

It is known that dihydro dicarboxylic acids of certain aromaticmonocyclic hydrocarbons undergo a molecular rearrangement when they areheated in an alkaline medium. For example, it is known that1,4-dihydroterephthalic acid may be heated in an alkaline solution so asto cause a molecular rearrangement to occur. The resultant product ofthe rearrangement is 3,6- dihydroterephthalic acid. I have discoveredthat rearrangements, which may be somewhat sim lar to the above referredto rearrangement, also occur when the so-called low melting dicarboxylicacids of dihydro polycyclic aromatic hydrocarbons having two benzenenuclei per molecule are treated with alkaline solutions. For example,the low melting dihydro dicarboxylic acids of diphenyl and naphthaleneor their substituted derivatives undergo rearrangements when they areheated in caustic soda solution so that products having differentproperties from the original acids are produced. I have furtherdiscovered that the rearrangement is accompanied by marked changes incertain properties of the acid, e. g., its solubility in water ismarkedly reduced and its melting point is appreciably raised.

The above objects which relate to the rearrangement of the so-called lowmelting acid are accomplished in accordance with the present inventionby treating the salt of the low melting acid, or a mixture of the saltsof the low and high melting acids, with an alkaline aqueous solution.This is carried out preferably by warming or boiling the solution of thesalt or salts in the presence of free alkali. Rearrangement of the lowmelting acid occurs during the alkali treatment to produce a producthaving a higher melting point and a markedly lower solubility in water.

It is believed that the acids primarily formed in carboxylating sodiumnaphthalene, for example, are 1,4-dihydro 1,4-dicarboxylic and 1,2-dihydronaphthalene 1,2-dicarboxylic acids and that rearrangement of thelatter acid occurs in the manner indicated by the following equation:

n coon coon H ooon coon H Although it is believed that the aboveequation indicates the type of rearrangement that occurs in the case ofthe so-called low melting acids during the alkali treatment, it is to beunderstood that the present invention is not limited by the abovesuggested mechanism of the rearrangement.

The following example illustrates the rearrangement of the low meltingdihydronaphthalene 1,2-dicarboxylic. acid.

Example II Dihydronaphthalene 1,2-dicarboxylic acid, 21.8 grams, whichmelted in the range of 172 to 183 C., was dissolved in 100 cc. of watercontaining 16 grams of caustic soda. The resultant solution was refluxedfor 5 hours and, after cooling, was treated with an amount ofhydrochloric acid equivalent to the quantity of caustic soda previouslyused. The acid which separated from the solution was recrystallized fromalcohol to give a product which melted at 240 C. Its solubility in waterwas 0.02 and 0.3 gram per 100 cc. of solution at 25 C. and 95-100 C.,respectively. The resultant high melting product had the sameneutralizing equivalent as the original low melting acid and uponoxidation with potassium ferricyanide by the method described in U. S.Patent 2,054,100, issued September 15, 1936 to Norman D. Scott andJoseph Frederic Walker, beta naphthoic acid was obtained.

The separation of dihydronaphthalene 1,4=dicarboxylic acid fromdihydronaphthalene 1,2-

dicarboxylic" acid is illustrated by thefollowing example.

Example III A mixture of the sodium salts of the above acids wasobtained by. carboxylating the sodium addition product of naphthalene.The mixed sodium salts were acidified with hydrochloric acid whichcaused a precipitate of the 1,4-dicarboxylic acid to form, while the1,2-dicarboxylic acid remained in solution due to its greater solubilityin water. The precipitate was washed thoroughly with water at 40 C.after which it Was digested with a small amount of water at C. andfiltered while hot in order to remove last traces of the 1,2-dicarboxylic acid. The filtrate containing the soluble 1,2-dicarboxylicacid was treated with a slight excess of caustic soda solution andboiled for 1 hour, after which the solution was cooled and acidifiedwith hydrochloricacid. The mixture was filtered and the separatedrearranged acid was washed with hot water.

The melting point of the precipitated 1,4-dicurboxylic acid was 219-227C. and thecrude rearranged dicarboxylic acid melted at ZOE-215 G. Sincethe solubility of the 1,2-dicarboxylic acid is markedly changed as aresult of the alkaline treatment, this change in its solubility makespossible a simple and easy method for isolating the acid from thereaction mixture in which it is prepared.

The following example illustrates the separation of mixed acids from areaction mixture in which they were prepared.

Example IV Naphthalene, 32 grams, was reacted with 16 grams of sodium in300 cc. of dimethyl glycol ether and the mixture carboxylated by themethod disclosed in my U. S.-Patent 2,033,056. The

unreacted sodium then was removed and weighed a and thesodium salts werefiltered off and dissolved in water.- To this solution was added a 1%caustic soda solution and the mixture was then heated to distill oiT anydimethyl glycol ether that had not been removed when the salts werefiltered. After the ether was removed, the alkaline solution wasrefluxed for 1 hour and then cooled and filtered to remove unreactednaphthalene. The filtrate containing the sodium salts of the reactionproducts was acidified with hydrochloric acid and the precipitatedmixture of acids was filtered off and dried. 26.6 grams of mixeddicarboxylic acids were obtained which corresponded to a yield of 69.5%of thetheory based upon the quantity of sodium consumed in the firstreaction. 'The mixed acids sintered at 200 C. and melted at 205 to 214C.

The most suitable alkalies for the present purpose are the alkali metalhydroxides. However, any alkali may be employed. since it is onlynecessary that the rearranging medium be alkaline in reaction. If themedium is only sl ghtly alkaline a longer time is required to efiect therearrangement than if a more strongly alkaline medium is employed. Inorder that the time required may not be unduly long, for example, longerthan about 1 to-5 hours, I prefer to use an amount of alkali equivalentto at least 2 grams of caustic soda .for every 100, grams of sodium saltof the dicarboxylic acid. My preferred quantities of alkali range from2-10 grams, calculated asca'ustic soda, for every grams of sodium saltbeing arrangement is not objectionable. Similarly, larger amounts ofalkali may be employed but in general there is no advantage in usingmore than 10 grams caIcuIated as caustic soda, for every 100 grams ofsalt.

The following experiment serves to illustrate the effect of, alkaliconcentration upon the extent to which rearrangement occurs duringrefluxing periods of hour and 3 hours.

Example V 7 100 cc. portions of the solution of mixed sodium salts weretreated with '1 and. 10 grams of caustic soda, respectively. The sampleswere refluxed for 3 hours after which the solutions were acidifled-andthe mixed acids, which were precipitated, were separated and theirmelting points determined. The extent of the rearrangement that occurredin each treatment is indicated by the weight of product obtained as wellas by the melting point of the product. The results are shown in thefollowing table:

, Refluxed for hour Refluxed for 3 hours Grams of caustic soda per 100cc. sample Grams of Melting Gram: .A'eltmg product point of productpoint of product product 0. o. (J 5. 3 198-203 J. 14. 3 203-2l9 17. 6209-219 10 15. 6 205-212 15. 4 2 1- 218 Although it is generallydesirable toeffect rearrangement by refluxing the alkaline solution ofthe salt or salts in order to shorten the time required to producecomplete rearrangement, rearrangement may be effected at temperaturesbelow the boiling temperature of the solution, for example, the solutionmay merely be warmed. Generally, when lower temperatures are used, amore alkaline solution is desirable in order to shorten, as much aspossible, the time required for complete rearrangement.

The rearrangement of dihydronaphthalene dicarboxylicacids, illustratedby the above examples, is also characteristic of the dihydrodicarboxylic acids of other polycyclic aromatic hydrocarbons which havetwo benzene nuclei per molecule. For example, when the alkali metaladdition product of diphenyl is reacted with carbon dioxide, it producesalkali metal salts of high and low melting dihydro dicarboxylic acids,similar to the high and low melting dihydro dicarboxylic'acids ofnaphthalene. As in the case o-f the low melting naphthalene derivative,the low melting dihydro dicarboxylic acid of diphenyl may be isolatedonly with difiiculty unless it is rearranged to form an insoluble acid.l

Therearrangement of the acids under consideration is "believed toinvolve a shift of a double bond andnot solely a stereo rearrangement.

But regardless of what actuallyoceurs during the rearrangement, itseffect is generally a lowering of the solubility of the acids in waterand a raising of their melting points. The decrease of the solubility inwater makes possible the separation in a practical direct manner ofindividual acids from the products produced by carboxylating an alkalimetal addition product of a polycyclic aromatic hydrocarbon having twobenzene nuclei per molecule, and also makes possible an easy andpractical method for separating mixed acids.

The exact structure of the rearranged acids has not been definitelyestablished. Such an accomplishment is exceedingly difficult due, notonly to the possibility of several structural isomers existing, butalso, to the probable existence of stereo isomers. Stereo isomerism mayoccur both in the acids originally obtained by carboxylating the alkalimetal hydrocarbon addition product as well as in the rearranged acids.However, it may be said that all indications so far obtained, relativeto the structure of the dihydronaphthalene 1,2-dicarboxylic acids,indicate that the rearrangement occurs in the manner shown in theequation presented above.

My invention is not limited to dihydro dicarboxylic acids of naphthaleneand diphenyl but includes any such acids of polycyclic aromatichydrocarbons which have two benzene nuclei per molecule. This includesdihydro dicarboxylic acids of substituted derivatives of thesehydrocarbons, e. g., alkyl naphthalenes and alkyl diphenyls.Accordingly, I use the terms naphthalene, diphenyl and polycyclicaromatic hydrocarbons having two benzene nuclei per molecule in theappended claims to include the substituted derivatives of suchhydrocarbons.

It would be obvious to any one skilled in the art that variousmodifications of my invention may be practiced without departing fromthe spirit and scope thereof. It is therefore understood that the scopeof my invention is not to be limited by the accompanying examples butonly by the scope of the appended claims.

I claim:

1. The process comprising heating a salt of a dihydrodicarboxyderivative of a polycyclic aromatic hydrocarbon having two benzenenuclei per molecule in an aqueous medium containing a quantity of alkaliequivalent to approximately 2-10 grams of caustic soda for every 100grams of said salt being treated.

2. The process comprising heating a salt of a dihydrodicarboxyderivative of a polycyclic aromatic hydrocarbon having twobenzene nucleipermolecule in an aqueous medium containing approximately 2-10 grams ofcaustic soda for every 100 grams of said salt being treated.

3. The process comprising heating a. salt of a dihydrodicarboxyderivative of naphthalene with an alkaline aqueous medium.

4:. The process comprising heating a salt of a dihydrodicarboxyderivative of naphthalene in an aqueous medium containing a quantity ofalkali equivalent to approximately 2-10 grams of caustic soda for every100 grams of said salt being treated.

5. The process comprising heating a salt of a dihydrodicarboxyderivative of diphenyl with an alkaline aqueous medium.

' 6. The process comprising heating a salt of a dihydrodicarboxyderivative of diphenyl in an aqueous medium containing a quantity ofalkali equivalent to approximately 2-10 grams of caustic soda for every100 grams of said salt being treated.

'7. The method of preparing a high melting substantially water insolubledihydronaphthalene dicarboxylic acid comprising heating a salt of a lowmelting, water soluble dihydronaphthalene dicarboxylic acid in anaqueous medium containing approximately 2-10 grams of caustic soda forevery 100 grams of said salt being treated and thereafter isolating saidhigh melting substantially water insoluble acid from said aqueousmedium.

8. The method of preparing mixed dihydronaphthalene dicarboxylic acidscomprising reacting naphthalene with an alkali metal and carboxylatingthe resulting alkali metal naphthalene addition compound, heating theresulting mixture of alkali metal salts of dihydronaphthalenedicarboxylic acids thus formed with an alkaline aqueous medium andthereafter acidifying the mixture to precipitate mixeddihydronaphthalene dicarboxylic acids.

9. The method of preparing mixed dihydronaphthalene dicarboxylic acidscomprising reacting naphthalene with sodium and carboxylating theresulting sodium naphthalene addition compound, heating the mixture ofsodium salts of dihydronaphthalene dicarboxylic acids thus formed withan aqueous medium containing 2-10 grams of caustic soda for every 100grams of said sodium salts, and thereafter acidifying the mixture toprecipitate mixed dihydronaphthalene dicarboxylic acids.

10. The method of separating high and low melting acids from thereaction mixture obtained by carboxylating an alkali metal additioncompound of a polycyclic aromatic hydrocarbon having two benzene nucleiper molecule comprising acidifying said reaction mixture and separatingthe high. melting dihydro dicarboxylic acid of said hydrocarbon, heatingthe aqueous solution obtained upon separation of said high melting acidin the presence of free alkali, and thereafter acidifying said solutionto precipitate a dihydro dicarboxylic acid.

11. The method of separating high and low melting acids from thereaction mixture obtained by carboxylating an alkali metal additioncompound of naphthalene comprising acidifying said reaction mixture andseparating the high melting dihydronaphthalene dicarboxylio' acid,heating the aqueous solution obtained upon separation of said highmelting acid in the presence of free alkali, and thereafter acidifyingsaid solution to precipitate a dihydronaphthalene dicarboxylic acid.

12. A method for separating high and low melting acids from the reactionmixture obtained by carboxylating a sodium addition compound ofnaphthalene comprising acidifying said reaction mixture and separatingthe high melting dihydronaphthalene dicarboxylic acid, heating theaqueous solution obtained upon separation of said high melting acid inthe presence of free caustic soda and thereafter acidifying saidsolution to precipitate a dihydronaphthalene dicarboxylic acid.

13. In a process for preparing dihydro dicarboxylic acids of polycyclicaromatic hydrocarbons having two benzene nuclei per molecule, the stepwhich comprises rearranging a dihydro dicarboxylic acid by heating withan alkaline aqueous medium.

14. As a new composition of matter, the mixture of dihydronaphthalenedicarboxylic acids prepared by heating a mixture of thedihydronaphthalene LZ-dicarboxylicanddihydronaphthalene 1,4-dicarboxylicacids primarily formed by carboxylating a sodium addition compound ofnaphthalene in the presence of an alkaline aqueous medium.

15. As a new compound, the dihydronaphthalene dicarboxylic acid preparedby heating the dihydronaphthalene 1,2-dicarboxylic acid pri- 10 marilyformed by carboxylating a sodium addition compound of naphthalene in thepresence of an alkaline aqueous medium.

16. As a new compound, 3,4-dihydronaphthalene 1,2-dicarboxylic acid,which compound has a melting point of approximately 240 C., issubstantially insoluble in water and which is oxidized by potassiumferricyam'de to beta naphthoic acid.

JOSEPH FREDERIC WALKER.

